#include <U8g2lib.h>
#include <Wire.h>
#include <qrcode.h>  //get library here -> https://www.arduinolibraries.info/libraries/qr-code

//U8X8_SSD1306_128X64_NONAME_HW_I2C disp(U8X8_PIN_NONE);  //use this line for standard 0.96" SSD1306
//U8X8_SH1106_128X64_NONAME_HW_I2C disp(U8X8_PIN_NONE);   //use this line for the SH1106 1.3" OLED often sold as 1.3" SSD1306
//U8G2_SH1106_128X64_NONAME_F_HW_I2C disp(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);
//U8G2_SH1107_128X128_1_HW_I2C disp(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);
//U8X8_SSD1306_128X64_NONAME_HW_I2C disp(U8X8_PIN_NONE);

/*
 * https://wokwi.com/projects/375224934099639297
 * https://github.com/olikraus/u8g2/wiki/u8g2reference#carduino-example
 *
 */

U8G2_SSD1306_128X64_NONAME_F_HW_I2C disp(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);

#define OLED_WIDTH 64
#define OLED_HEIGHT 64
#define STRLEN 16

uint16_t writecount = 0;
uint32_t startwritemS, endwritemS, timemS;

static char header[STRLEN];
static char message[STRLEN];

void loop() {
    writecount++;

    sprintf(message, "%03d", random(17, 30));
    sprintf(header, "%s", "PM2.5");

    disp.clearBuffer();
    disp.setFont(u8g2_font_6x13_tr);
    disp.drawStr(72, 12, header);

    displayQRCode(message);
    disp.sendBuffer();

    delay(random(900, 15000));
}

void setup() {
    disp.begin();
}

void displayQRCode(char * text) {
    QRCode qrcode;
    uint8_t qrcodeData[qrcode_getBufferSize(3)];
    qrcode_initText( & qrcode, qrcodeData, 3, 0, text);

    double scale = 1.6; //min(OLED_WIDTH / qrcode.size, OLED_HEIGHT / qrcode.size);

    int shiftX = 0;     //(OLED_WIDTH - qrcode.size * scale) / 2;
    int shiftY = 18;    //(OLED_HEIGHT - qrcode.size * scale) / 2;

    disp.setFont(u8g2_font_helvR24_tf);
    disp.drawStr(70, 42, text);

    for (uint8_t y = 0; y < qrcode.size; y++) {
        for (uint8_t x = 0; x < qrcode.size; x++) {
            if (qrcode_getModule( & qrcode, x, y)) {
                disp.drawBox(shiftX + x * scale, shiftY + y * scale, scale, scale);
            }
        }
    }
}